The invention described here relates to a mill having a stationary collision member that is arranged around a rotor that rotates about a vertical axis of rotation, by means of which material, in particular a stream (bundle) of granular materials is accelerated with the aid of an acceleration unit and propelled outwards from said rotor with, in particular, the aim of allowing the material to collide in an essentially deterministic manner—or at an essentially predetermined collision location, at an essentially predetermined collision angle and at an essentially predetermined collision velocity with said collision member, said material being loaded in such a way that it breaks or is comminuted in a manner that (as far as possible) is predetermined—i.e. (as far as possible) is deterministic; the determinism essentially not being affected by the wear which takes place on said collision member.
For the invention described here it is important to establish that—under the conditions described here—it is essentially physically impossible to propel material outwards from a rotor with only a radial (or only a transverse) velocity component. Under normal conditions the take-off angle is between 25° and 50°. It is therefore physically also impossible—under the conditions described here—to propel material outwards from a rotor along a straight radial stream (absolute take-off angle α=90°), viewed from a stationary standpoint; as is often (instinctively) suggested, including in the patent literature. The movement that material makes when it is accelerated in a rotating system—or under the influence of centrifugal force—is frequently incorrectly, or physically inaccurately, described The reason for this is that it is apparently difficult to imagine such a movement; which movement can (must) be regarded from a Stationary find a co-rotating standpoint at the same time. Instinctively one rapidly reaches an incorrect interpretation, A typical example of such a (physically inaccurate) conception of the state of affairs can be found in DE 39 26 203 A1 (Trapp) which describes movement of grains of the material from the central section of a rotor towards the outer edge of said rotor, which movement of grams actually takes place in the reverse direction. In the known single impact crushers the material is accelerated with the aid of acceleration members, which are carried by a rotor and are provided with radially (or forwards or backwards) oriented acceleration surfaces and propelled outwards at high velocity—under a take-off angle of 35° to 40°—against a stationary collision member in the form of an armoured ring made up of anvil elements, which is arranged around the rotor a relatively short distance away. The collision surfaces of the stationary collision member are generally so arranged that the collision with said stationary collision member as far as possible takes place perpendicularly. The consequence of the specific arrangement of the Collision surfaces of the individual anvil elements—at an angle—which is necessary for this is that the armoured ring as a whole has a type of knurled shape with projecting comers. Such a device is disclosed in U.S. Pat. No. 5,921,484 (Smith, J, et al.).
The collision surfaces of the individual anvil elements of the known single impact crushers are often straight in the horizontal plane, but can also be coed, for example in accordance with an evolvent of a circle. Such a device is disclosed in U.S. Pat. No. 2,844,331. What is achieved by this means is that the impacts all take place at the same (perpendicular) angle of impact. U.S. Pat. No. 3,474,974 discloses a device for a single impact crusher in which the stationary impact surfaces are oriented obliquely downwards in the vertical plane, as a result of which the material rebounds downwards after impact. What is achieved in this way is that the angle of impact is more optimum, the impact of subsequent grains is less disturbed by breakage fragments from previous Impacts and the breakage fragments do not rebound against the edge of the rotor.
U.S. Pat. No. 5,860,605, in the name of the Applicant, discloses a method and device for a direct multiple impact crusher (SynchroCrusher) which is equipped with a rotor which rotates about a vertical axis of rotation, by means of which the material is accelerated in two steps, i.e. guiding along a relatively short guide member and, respectively, an (entirely deterministic) blow by a co-rotating impact member, in order then to allow it to collide with a stationary collision member, for example in the form of individual evolvent collision elements (with projecting Joints) which are arranged around the rotor and which have the effect of causing the material to strike perpendicularly. Loading takes place in two immediately successive (synchronised) steps. The second collision takes place at a velocity, or kinetic energy, which remains after the first impact; that is to say without additional energy having to be added. Said residual velocity is usually at least equal to the velocity at which the first impact takes place.
U.S. Pat. No. 2,357,843 (Morrissey) discloses an impact crusher with which a Stationary collision member is arranged around the rotor a short distance away, the collision surface of which collision member is cylindrical; here it is suggested that the material is propelled radially outwards from the rotor, which, as has already been explained, is physically impossible (inaccurate) under the indicated conditions because, in addition to a radial velocity component, the material also builds up an appreciable (usually even greater) transverse component along the guide member.
PCT/WO 94/29027, in the name of the Applicant, discloses an impact crusher with which the material is propelled from the rotor against the inside of a first stationary conical ring that widens towards the bottom and is arranged around the rotor, a short distance away, the intention being that the material strikes the collision ring in a virtually radial direction and then rebounds obliquely downwards in a virtually radial direction against the outside of a second stationary conical ring that widens towards the bottom and is arranged below the rotor, after which the material continues to move downwards in a zig-zag bouncing movement through the slit-shaped gap between the conical rings in the virtually vertical direction. The distance between the two collision surfaces can be adjusted to some extant in that the height of the outer ring is adjustable. It is suggested that the material is propelled outwards from the rotor, which is equipped with guides curved severely backwards, in a virtually radial directions with the aim of impinging virtually perpendicularly (radially) on the first stationary conical ring, viewed from the plane of rotation The optimum angle of impact of approximately 70° is obtained with the aid of the conical shape of the Collision surface. As already indicated, it is, however, physically impossible to propel the material outwards from the rotor in this way in a radial direction (take-off angle a of approximately 90°), with such an arrangement of the guide and collision element the take-off angle (α), and thus the angle of impact, is actually much smaller (approximately 45°) and during impact on the conical ring there can essentially be said to be a glancing blow, the material being subjected to only limited loading and continuing to rebound in the plane of rotation; and starts to describe a glancing circular (spiral) movement oriented obliquely downwards in the slit-shaped gap.
G 90 15 362.6 (Gebrauchsmuster DE-Pfeiffer) discloses an impact crusher with which a stationary collision member is arranged around the rotor, which collision member is so constructed that the distance between the outer edge of the rotor and the collision surface is adjustable.
JP 4-100551 (Kuwabara Tadao et al.) discloses an impact crusher equipped with a rotor around which a stationary collision member is arranged in the form of an armoured ring made up of so-called anvil blocks, each of which is equipped with an impact surface that is oriented perpendicularly to the path that the material describes when it is propelled outwards from the rotor. The armoured ring as a whole consequently has a knurled shape with projecting comers. In the known impact crusher the radial distance (L) between the projecting points of the anvil blocks and the outer edge of the rotor is chosen so large that, on the one hand, as little material as possible rebounds against the outer edge of the rotor after the collision, so that wear at this edge is restricted, and, on the other hand, a good degree of comminution is nevertheless obtained. On the basis of an investigation that was carried out, the data of which are incorporated in JP 4-100551, the length L was determined as 250-350 mm for a circumferential velocity of the rotor of 50-70 m/sec. The diameter of the rotor, the diameter of the armoured ring and the take-off angle (α) were not taken into account in the investigation.
U.S. Pat. No. 5,863,006 (Thrasher, A) discloses an autogenous impact crusher that is equipped with a rotor by means of which the material is, as it were, autogenously accelerated, as a result of which wear is restricted. The autogenous rotor does, however, easily become unbalanced and is therefore equipped with an auto-balancing system in the form of a flat hollow ring that is arranged around the top edge of the rotor and is filled with oil and steel balls. This auto-balancing system has already been known for a long time (since 1880 from U.S. Pat. No. 229,787, Whitee). Recent publications relate to Julia Marshall: Smooth grinding (Evolution, business and technology magazine, SKF, No, 2/1994, pp. 6-7) and Auto-Balancing by SKF (publication 4597 E, 1997-03).
U.S. Pat. No. 4,389,022 (Burk) discloses a single impact crusher that is equipped with an annular collision member in the form of a sort of polygon with regular offsets, the individual line sections forming straight impact surfaces, the distance of which from the axis of rotation is alternately offset, as a result of which a sort of knurled polygon edge is formed. The collision surfaces of the line sections are arranged directly around the rotor and, when these wear, can be moved forwards, that is towards the axis of rotation.
In 1999 Nordberg marketed a single impact crusher that is equipped with a rotor which rotates about a vertical axis (Nordberg VI series, brochure number 0775-04-00-CED/Macon/English, 2000), the stationary impact member being constituted by an annular armoured member that is arranged around said rotor a relatively short distance away, which armoured member is made up of hollow cylinders which are positioned some distance apart alongside one another in a circular shape, each of which cylinders can be rotated (is adjustable) about its cylinder axis that runs parallel to the axis of rotation of the rotor. The stationary impact surface consequently does not have a knurled shape but has the shape of a number of segments in the form of an are arranged alongside one another in a circle. This has the advantage that the cylinders can be turned, so that the (entire) wear surface can be consumed. However, the impacts take place highly irregularly because the grains strike said are segments at highly divergent angles—from perpendicular to glancing blow—whilst some of the impacts can be disturbed or damped by the material itself that can settle between the are segments.